Interpretive Summary: In the case of a crisis event involving illnesses due to an unknown chemical adulterant in food, analytical methods are needed to determine which chemical may be causing the illnesses. Due to its potential to cause fevers, lipid A endotoxin is one such chemical that should be included among those monitored in food emergency response situations. Until now, no analytical method has existed to monitor for lipid A in foods because it has unique properties and a greater molecular weight that make it difficult to determine using typical techniques designed for smaller molecules. In this work, we developed a new rapid method involving supercritical fluid chromatography coupled to tandem mass spectrometry. This provides the ability to monitor for an additional chemical contaminant when an outbreak of foodborne illness occurs due to an unknown source.

Technical Abstract:
Food safety and defense applications require the availability of methods of detection for a variety of toxic compounds in foods. One compound of concern is lipid A, an endotoxin from Gram-negative bacteria, which can cause human illness if it is present at acutely toxic levels in food. The chosen lipid A analyte was a form derived from Salmonella Minnesota, R595 and exhibited both hydrophilic and hydrophobic characteristics due to phosphate and fatty acid functional groups. In this study, a novel approach was developed to quantitatively monitor lipid A without chemical modification from representative food matrices (lettuce and ground beef) using supercritical fluid chromatography (SFC) coupled with an ion-trap mass spectrometer (MS/MS). For extraction, a solvent combination of 75% chloroform and 25% methanol was used in a simple shaking procedure. Lipid A partitioned into the chloroform layer, which separated from the aqueous layer introduced by the food sample. The chloroform sample extract was then analyzed without further cleanup. The total instrument analysis time is only 2 min for each injection. In spiked samples, %recovery of lipid A from lettuce averaged 74 +/- 10 at concentrations ranging from 10-30 ug/g (n=14). Due to co-extractives in ground beef, the detection limit was higher and %recovery obtained was 110 +/-5 at 30 ug/g. This study demonstrated the feasibility of using SFC-MS/MS for a targeted screen of lipid A in a simple, fast, economical, and environmentally-friendly approach.